Polyhedral cells

Fig. 25.8. Poly meric foams, showing the polyhedral cells. Some foams hove closed cells, others hove cells which ore open.

The so-called bi-liquid foams described by Sebba and Vincent [17-20] will not be discussed since they are not true colloidal emulsions, but resemble conventional foams more closely, possessing polyhedral cells of centimetre dimensions. 

As was mentioned in the introduction, HIPEs contain an internal phase volume fraction greater than 0.74. Since this is the maximum volume which can be occupied by uniform, undeformed spherical particles, the dispersed phase droplets must either be non-uniform, i.e. polydisperse, or deformed into non-spheri-cal, polyhedral cells. 

The corneal epithelium in itself is also a layered structure, 50-100 pm thick, consisting of a deep layer of basal columnar cells, an intermediate layer of polyhedral cells, and a surface layer of squamous, polygonal-shaped cells. The outermost cells have skirting intercellular junctions, termed tight junctions (Figure 25.3). These form a strong barrier to nonlipophilic substances, allowing the preferential penetration of nonionized forms. 

The mouth and esophagus are composed of two layers, the mucosa and submucosa (Figure 3.5). The mucosa is lined on its outer surface by a stratified squamous epithelium with layers of polyhedral cells of the intermediate layers and low columnar cells of the basal layer. Below the cellular layer is the lamina propria containing loose connective tissue with blood vessels and small aggregates of lymphocytes. Smooth muscle within the mucosa (muscularis mucosal layer) is seen as small bundles. The submucosa... 

A transmission electron micrograph of a composite whose composition is given in Table 7 is presented in Fig. 33. This figure shows that the dispersed phase is composed of polyhedral cells of polyacrylamide separated by films of polystyrene. The obtained material is white, soft, and exhibits some elasticity. 

Cross-linked polystyrene porous particles (with 21 mol% DVB) have been prepared by the concentrated emulsion polymerization method, using either toluene or decane as the porogen and an aqueous solution of SDS as the continuous phase. Since toluene is a good solvent for polystyrene while decane is a nonsolvent , the morphologies obtained in the two cases were different. The particles based on toluene (with a volume fraction of dispersed phase of 78%) have very small pores which could not be detected in the SEM pictures. The pore size distribution, which has sizes between 20 and 50 A and was determined with an adsorption analyzer, almost coincides with that in a previous study [49] in which porous polystyrene beads have been prepared by suspension polymerization. In contrast, the porous particles based on decane have pore sizes as large as 0.1-0.3 pm, which could be detected in the SEM pictures [44a], and also larger surface areas (47 m2 g ) than those based on toluene (25 m2 g ). The main difference between the concentrated emulsion polymerization and the suspension polymerization consists of the much smaller volume fraction of continuous phase used in the former procedure. The gel-like emulsion that constitutes the precursor in the former case contains polyhedral cells separated by thin films of continuous phase. The polymerization of the cells does not... 

Epidermis, a protective outer covering tissue, composed of a single layer of brownish polyhedral cells from which are given off scaly hairs. 

The sequence of events on the colloidal level corresponding to the five macroscopically observable stages outlined above has been deduced from the nature of the gel network in the finished membrane (, ) and from the ghosts of the nascent membranei that is, the frozen and lyophilized nonvolatile remnants of the membrane in its Various formative phases ( ). The polyhedral cell structure of the final membrane gel is considered to be an Immobilized and flattened version of the sol precursors which exists in the solution immediately prior to the sol-gel transition. As the loss of volatile solvent progresses, the solvent power of the solution decreases that is, its capability for retaining the polymer in a homogeneous single phase Sol 1 solution is diminished. If only polymer and solvent are present, then at least three situations are possible ... 

It is seen in Fig.2 that both FT process and FN one result in formation of nanostructure consisted of polyhedral cells/blocks of different sizes. 

Figure 12.13 Photograph of a foam showing the polyhedral cells bounded by plane faces.

The whole of three-space is divided up into polyhedral cells, each containing one atomic nucleus at its centre and the integration is performed outwards" from each nucleus up to the boundaries of the cells. 

Foam structure and dynamics. Surface layers surrounding the bubbles in a foam act as a membrane or skin that can stretch and relax in response to the lateral forces acting on it. At first, drainage of liquid taking place at the surface layer is entirely hydrod)niamic, but once spherical bubbles are in contact, flat walls develop between them, and polyhedral cells appear in the foam (Fig. 14.9c). Capillary forces be-... 

The succeeding outer layer is the stratum spinosum, or prickle cell layer it consists of several layers of irregular polyhedral cells (Figure 1.2, Figure 1.4). These cells are connected to adjacent stratum spinosum cells and to the stratum basale cells... 

Upon replacing the polyhedral cells (a) by overlapping spheres (Figure 2.38(b)), the problem has already become slightly easier to solve, but it still suffers from a discontinuous potential derivative at the sphere boundaries thus, a more comfortable situation is enforced by setting up a muffin-tin potential (c), with an atomic-like shape close to the nucleus and a zero potential inbetween. 

Figure 1 shows the cellular structure of a typical PP foam, which was manufactured by molding PP foam beads with superheated steam. Each bead consists of closed polyhedral cells, with no visible accumulation of material in the comers. The PP foam beads themselves are melted together at their surfaces and form a secondary cellular structure. 

Finally, in this section, the enormous importance of natural gas water hydrates should be briefly mentioned. These hydrates are polyhedral cells consisting of H-bonded waters and stabilized by encaged guest molecules such as methane and carbon dioxide. These solid hydrates constitute a great problem in gas transmission lines and inhibitors for their formation have been developed. ... 

Foam is an agglomeration of a large number of different bubbles (Plate 4.13). Each bubble in the foam is a polyhedral cell with a number of different faces. Each face is curved as a result of the excess pressure across it. If the pressure in two adjacent cells is the same, the excess pressure across the surface is zero and the separating surface is planar. The foam will contain, only, three film surfaces intersecting along lines at 120° and four lines of soap film meeting at a point with adjacent lines intersecting at 109° 28. ... 

If each face of the regular polyhedron, which is an approximation to the average polyhedral cell, has n sides and the angles at the corners of the faces are assumed to be d, then the sum of the angles of the -edged polygon is... 

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